1. Field of the Invention
This invention relates to an apparatus and method for separating various materials. In particular, this invention relates to improvements in a conveyer with a unique disc screen that improves the screen""s performance and reduces maintenance thereof.
2. Description of the Related Art
Disc or roll screens, as contemplated by the present invention are frequently used as part of a multi-stage materials separating system. Disc screens are used in the materials handling industry for screening large flows of materials to remove certain items of desired dimensions. In particular, disc screens are particularly suitable for classifying what is normally considered debris or residual materials. This debris may consist of various constituents. It may contain soil, aggregate, asphalt, concrete, wood, biomass, ferrous and nonferrous metal, plastic, ceramic, paper, cardboard, or other products or materials recognized as debris throughout consumer, commercial and industrial markets. The function of the disc screen is to separate the materials fed into it by size. The size classification may be adjusted to meet virtually any specific application.
Disc screens generally have a screening bed having a series of rotating spaced parallel shafts each of which has a longitudinal series of concentric screen discs separated by spacers which interdigitate with the screen discs of the adjacent shafts. The relationship of the discs and spacers on one shaft to the discs and spacers on each adjacent shaft form an opening generally known in the industry as the interfacial opening or xe2x80x9cIFOxe2x80x9d. The IFOs permit only material of acceptable size to pass downwardly through the rotating disc bed. The acceptable sized material which drops through the IFO is commonly referred to in the industry as Accepts or Unders.
The discs are all driven to rotate in a common direction from the infeed end of the screen bed to the outfeed or discharge end of the bed. Thus, materials which are larger than the IFO, referred to in the industry as Overs, will be advanced on the bed to the outfeed end of the bed and rejected.
A major problem with such disc screens is jamming. Where the discs are not in line, material tends to jam between the disc and the adjacent shaft, and physically forcing the screen to stop. This phenomenon can be deleterious to the conventional disc screen. Although the jamming phenomenon may not cause the roll screen to stop completely, it may cause momentary stoppages. Such stoppages may not cause the drive mechanism of the roll screen to turn off but they may cause substantial mechanical shock. This mechanical shock will eventually result in the premature failure of the roll screen""s roll assemblies and drive mechanism.
Another problem with disc screens is effectively separating debris having similar shapes. It is difficult to separate office sized waste paper (OWP) since much of the OWP has the same long thin shape. For example, it is difficult to effectively separate notebook paper from old corrugated cardboard (OCC) since each is long and relatively flat. A secondary slot is typically formed between the outside perimeter of discs on adjacent shafts. OWP is difficult to sort effectly because most categories of OWP can slip through the secondary slot.
Accordingly, a need remains for a system that classifies material more effectively and while also being more resistant to jamming.
The invention concerns an apparatus for classifying material by size. It comprises a frame, a plurality of shafts mounted on the frame substantially parallel with one another and defining a substantially planar array, means for rotating the shafts in ganged relation to one another, and a plurality of discs mounted on the shafts in a substantially coplanar row, each of the discs having a perimeter shaped to maintain the space between discs substantially constant during rotation.
In accordance with this invention, we disclose a method for classifying material by size. This method comprises defining a plurality of substantially uniform openings disposed between a plurality of shafts arranged to define a substantially planar array, mounting noncircular discs on the shafts in substantially parallel rows, rotating the shafts in the same direction, dropping the material on the shafts at one side of the array so that shaft rotation causes the material to be pushed by the discs across the remainder of the shafts in the array, and maintaining the spacing between discs in a row substantially uniform during rotation.
In an alternative embodiment of the invention, we disclose an apparatus for classifying material by size which includes a frame; a plurality of shafts mounted on the frame substantially parallel with one another; a first stage including discs mounted on the shafts in a substantially coplanar row, each of the discs having a perimeter shaped to maintain the space between discs substantially constant during rotation; and a second stage including discs mounted on the shafts in a substantially coplanar row, each of the discs having a perimeter shaped to maintain the space between discs substantially constant during rotation. The first stage discs are positioned to allow passage of only small fraction material and the second stage discs are positioned to allow passage of intermediate fraction material and thereby classifying the material into a small fraction, an intermediate fraction and a large fraction.
In another embodiment of the invention, a unique screen arrangement increases separating efficiency by moving materials over multiple separation stages. A receiving section agitates debris while the debris moves at an angle up to a given elevation. The agitation of the debris in combination with the angled upward movement promotes separation of the large and small sized materials. A roll over section drops the materials down to a discharge position for feeding onto a discharge section. The materials are dropped from the roll over section so that the debris either falls vertically downward or flips over further promoting separation. The discharge section again agitates the debris while moving up a second incline until the larger debris discharges out a rear end.
The discs are interdigitized at the front end of the receiving and discharge sections to prevent large materials from falling between the rows of discs. Shafts on the different sections also have separately controllable rotation speeds allow larger materials to be quickly moved out from underneath materials previously dropped from the roll over section.
In yet another embodiment of the invention, a compound disc is used to eliminate secondary slots formed between the outside perimeter of discs on adjacent shafts in a material separation screen. The compound disc comprises a primary disc joined to an associated secondary disc. The primary disc and the secondary disc each have the same shape but the secondary disc has a smaller outside perimeter and is wider. The primary disc and associated secondary disc are formed from a unitary piece of rubber.
The compound discs are interleaved with oppositely aligned compound discs on adjacent shafts. In other words, the large disc is laterally aligned on a shaft with a smaller disc on an adjacent shaft. The alternating arrangement between the large discs and small discs eliminate secondary slots that normally exist in disc screens. The rubber disc provide additional gripping for flat materials such as paper while allowing oversized materials, such as plastic bottles, to roll off a bottom end of the screen. Thus, the compound disc separates materials more effectively than current disc screens while also reducing jamming.
The foregoing and other objects, features and advantages of the invention will become more readily apparent from the following detailed description of a preferred embodiment of the invention which proceeds with reference to the accompanying drawings.